The present invention relates to functional fluid compositions containing antioxidants, and specifically stable compositions containing antioxidants with limited solubility in and/or limited compatibility with the functional fluids with which they are used.
Antioxidants and their importance to various types of functional fluids are known. However, many antioxidants may only be used in limited ways due to solubility and/or compatibility issues with the functional fluids in which they are used. Many antioxidants, including phenolic or benzoic antioxidants, have limited solubility in functional fluids, such as engine oils, gear oils and greases. These antioxidants, when used at levels above their solubility and/or compatibility limits, may fall out of the functional fluid composition over time and/or cause the composition to appear hazy or cloudy.
These are serious issues in the manufacturing and blending processes of the fluids as well as in the field. For example, a functional fluid additive manufacturer would sell a homogeneous additive package of performance chemicals, which may then be added to a base oil to give a final lubricant, which in turn is sold in tanks, drums, cans and plastic containers for final delivery of the lubricant to the equipment to be lubricated. To maintain assurance of performance of the final lubricant, or any other functional fluid, in the equipment in which it is used, the concentrate and the lubricant must remain homogeneous throughout these steps. In other words, all of the additives present must be compatible with each of the various materials it comes into contact with and/or finds itself, from the additive package to the concentrate to the final fluid. This stringent standard greatly limits the choices of and available treatment levels for many additives, including the antioxidants discussed herein. These antioxidants could provide improved performance to a functional fluid but are not widely used and/or are not used at the optimal level because the additive does not meet the solubility and/or compatibility requirements discussed above.
In the field, functional fluid compositions that drop out one or more components over time may not perform properly unless they are well-mixed before use, or may be removed by filters associated with the equipment in which the functional fluid is used. The haziness and/or cloudiness of a functional fluid, which may be measured as the fluid's turbidity, is often seen as a sign the composition is not stable, or may be in an early stage of separation and/or component drop out. Such conditions are not desired in functional fluid compositions, for both performance and aesthetic related reasons. This reality has created constraints on the use of various antioxidants, such as effective maximum treat rates.
Without these solubility and/or compatibility limitations on the use of these antioxidants, greater performance and equipment protection might be achievable, including for example extended life of a lubricant or a lubricated piece of equipment such as engines, automatic transmissions, gear assemblies and the like. Improved fuel economy and viscosity stability might be achievable as well. Greater performance may even be achievable with lesser amounts of chemical as well as greater amounts, depending on the selection of the more effective, but otherwise not suitable chemicals from a compatibility or solubility standpoint when delivered in a conventional manner.
There is a need for functional fluid compositions that contain higher amounts of antioxidants while still remaining stable and/or clear. There is particularly a need for functional fluid compositions, such as engine oil compositions, that contain phenolic or benzoic antioxidants, at levels that would otherwise cause the composition to be unstable and/or hazy, as described above. The compositions and methods of the present invention overcome these constraints and thus allow the use of these antioxidants at levels not otherwise possible while still maintaining the stability and/or clarity of the functional fluid composition.